This invention relates to improvements in ladders and refers particularly, though not exclusively, to devices for attachment to ladders for improving the safety of the ladders when used.
Ladders have been used by mankind for countless centuries. Throughout their history the basic design and concept have remained unchanged. There have been some improvements such as the extension ladder and step ladders but the standard, everyday ladder has remained virtually unchanged. From basic geometry it can be ascertained that if a 30 foot long ladder is 5.degree. off-angle then the top of the ladder is quite a distance from its correct position.
One of the major problems with ladders is their inherent instability when used on anything other than a horizontal plannar surface. In fact, when used on irregular and/or sloping surfaces the need for blocks and the like makes the use of a ladder extremely dangerous and, also, very time consuming. Also, when resting against smooth surfaces their tendency to slide can be rather dangerous. These have caused serious problems regarding the safety of persons using ladders. The large number of accidents both domestic and industrial each year is evidence of this. However, other than attempting to train the user of ladders, nothing has been done to overcome the problems. When one considers the cause of the accidents--the ladder itself--there has been nothing done in this regard. The basic design of ladders has never changed.
Many attempts have been made over the years to solve the well known problems which plague ladders and their use. Two such examples are those shown in the specifications of U.S. Pat. Nos. 983,172 of Sheetz and No. 973,509 of Ison, dated Jan. 31, 1911 and Oct. 25, 1910, respectively. These show complex and large structures designed to be attached to the lower rungs of the ladder. These devices both work off very similar principles but their constructions vary slightly. However, in each case these are good reasons why the devices shown are impractical--they are unsafe and do not comply with the basic requirements of such devices.
It is well known that a standard ladder has two rails and a number of rungs. It is required that the bottom rung be no more than 12 inches above the ground. As can be seen, neither of the Ison or Sheetz devices comply with this requirement. Furthermore, the rails of a ladder are far more capable of bearing loads than the rungs. With both the Sheetz and Ison devices, the rungs must bear not only the weight of a person using the ladder but also the weight of the ladder itself. This is, naturally, very unsafe. Furthermore, the devices of Sheetz and Ison are only suitable for use on soft ground due to the nature of the ground contact feet--they could not be used on paved surfaces or indoors.
Further devices are shown in the specifications of U.S. Pat. Nos. 2,205,935 of Stenroos and No. 2,960,182 of Swanson. The Swanson device has an arcuate tubular member which supports the rails and one rung of the ladder. A slip-lock device is used to hold the ladder in position relative to the tubular member. This device does not satisfy the basic safety requirements for devices for angular adjustment of ladders. The stenroos device is attached to the ladder in a manner very similar to that of Swanson but uses a series of alignable holes in three plates for providing the angular adjustment. Apart from the problems associated with all of the above described prior devices, the Stenroos device also has the problem that it requires a considerable effort for a user to adjust the device after moving from one locale to another.
Further, the calibration of most of these devices has been such that the control of the ladder is to within only approximately 5.degree.--this being totally unsatisfactory.